A two year in vitro study is being proposed to bacteriocin type Strep. mutans isolates obtained from mother-infant pairs. The subject pairs will be selected from the experimental population employed in the initial phase of this research program (funded by N.I.D.R. Grant 1 R23DE05357-01). Approximately 391 test Strep. mutans isolates, obtained from 23 mother-infant pairs, will be characterized by their bacteriocin production and sensitivity patterns. The bacteriocin codes of the test strains within each mother infant pair will be compared to assess the likelihood that maternal transmission was the route for primary infant infection. Should this hypothesis be experimentally substantiated, future research efforts would be directed at identifying mothers at risk for infecting their infants and clinically suppressing their Strep. mutans reservoirs. This approach, in turn, should decrease the frequency of Strep. mutans infection of infancy thereby decreasing the incidence of dental caries during the first two years of life.